Ok to do elbows from side mount just press the left stick in any direction and hit the punch button that corresponds with the side you are on. E.g. Left punch for left side mount and right punch for right side mount.
As for the legs kicks slowing your opponent down....it seems to work for me. It also definitely mentions something about this in the tutorial. Also it's supposed to make their kicks slower/weaker as well. Same goes for if they block your high strikes their punches will become weaker/slower.
Just got a new best time for a knockout. 10 seconds into the 1st with Chuck. Leg kick, Leg kick, superman punch, and goodnight Shogun.